Welcome to the webpage for the Workshop on Macroscopic Superpositions of Levitated Systems to be held at the Centre for Quantum Technologies at the National University of Singapore.
The workshop concerns both the theoretical and experimental aspects of this subject. It aims to build connections between young scientists and promotes open discussions between participants. As such, all participants will give 30-minute talks and there will full days for discussion. The schedule of the workshop consists of invited talks in the first two days, a session within the Institute of Physics Singapore Meeting (ipsmeeting.org) on Wednesday, and two days free for discussions.
Invited speakers
Andreu Riera-Campeny – ICFO – The Institute of Photonic Sciences, Barcelona, Spain
Andrew Dana – Northwestern University, United States
Anupam Mazumdar – University of Groningen, Netherlands
Daniel Kodroff – Lawrence Berkeley National Laboratory, United States
Dennis Uitenbroek – Leiden University, Netherlands
Eli van der Bent – Leiden University, Netherlands
Kim Daehee – Okinawa Institute of Science and Technology, Japan
My affiliation is the Quantum Machines Unit at the Okinawa Institute of Science and Technology Graduate University (OIST) in Okinawa, Japan. OIST is a graduate-only, fully English-speaking university established by the Japanese government in 2011. It operates without traditional academic departments; instead, research is organized into interdisciplinary Units, each led by a faculty member. These Units span a broad range of topics across science and technology, fostering collaboration across disciplines.
I am a PhD student from Korea, currently in the fourth year of a five-year doctoral program. My research involves simulations and experiments focusing on the magnetic levitation of objects and the study of their rotational dynamics. While such levitated rotors have potential applications in precision sensing—such as gyroscopes—our primary goal is to develop systems with ultra-low rotational damping and to achieve precise control over their motion, ultimately pushing them toward the quantum regime.
Marko Toros – University of Ljubljana, Slovenia
Martine Schut – National University of Singapore
After completing a PhD at the University of Groningen on gravity-induced entanglement experiments, I started a postdoc at the National University of Singapore in January this year to continue my work on coherence loss in macroscopic quantum systems and quantum information and start research on creating quantum superpositions in macroscopic objects.
Matteo Fadel – ETH Zurich, Switzerland
Nancy Gupta – University of Vienna
Panyu Hou – Tsinghua University, China
Assistant professor at Center for Quantum Information, Tsinghua University. I am an experimentalist, working with trapped ion for large-scale quantum computing and quantum simulation, as well as nitrogen-vacancy centers for quantum network and quantum sensing.
Qiongyuan Wu – King’s College London, United Kingdom
Stefan Nimmrichter – University of Siegen, Germany
Tim Martijn Fuchs – University of Southampton, United Kingdom
Xueqi Ni - National University of Singapore
Yin Peiran – Nanjing University, China
Dr. Peiran Yin earned his Ph.D. in 2020 from the CAS Key Laboratory of Microscale Magnetic Resonance at the University of Science and Technology of China, under the supervision of Professor Jiangfeng Du. Currently, he serves as an Associate Researcher at Nanjing University in Professor Huang Pu’s laboratory. His research focuses on developing experimental techniques with magnetically levitated systems for fundamental physics investigations, including tests of beyond-standard-model forces, high-precision gravity measurements, and ground-state cooling.
Zhang Huaijin – Beijing Institute of Technology, China
The main subject of the workshop is the creation of macroscopic superpositions in levitated systems, which includes, for example, topics such as cooling techniques, mechanical resonators, levitation, trapping, coherence loss and optomechanics with nanospheres
Schedule
Welcome to the Workshop on Macroscopic Superpositions of Levitated Systems
Coffee and Tea at the Quantum Cafe
The mechanical motion of a diamond that is levitated in a vacuum can be coupled with the spin states of color centers, such as nitrogen-vacancy centers, within the diamond lattice. Consequently, the spatial superposition of the diamond can be realized by manipulating these spin states. Based on this principle, we have proposed a matter-wave interference scheme and explored its potential applications in the field of quantum sensing.
Atomic ions trapped in ultrahigh vacuum provide a versatile platform for universal quantum computing and quantum simulations of various physical models. Here, I will talk about our recent observation of quantum superposition of topological defects in a trapped-ion quantum simulator. By engineering long-range spin-spin interactions, we observe a spin kink splitting into a superposition of kinks at different positions, creating a “Schrodinger kink” that manifests nonlocality and quantum interference. Furthermore, by preparing superposition states of neighboring kinks with different phases, we observe the propagation of the wave packet in different directions, thus unambiguously verifying the quantum coherence in the superposition states. Our work provides useful tools for nonequilibrium dynamics in quantum Kibble-Zurek physics.
Lunch at the Frontier Food Court (vegetarian options available)
Levitated optomechanics, the interaction between light and small levitated objects, is a new macroscopic quantum system that is being used as a testing ground for fundamental physics and for the development of sensors with exquisite sensitivity. The utility of this system, when compared to other quantum optomechanical systems, is its extreme isolation from the environment and, by the relatively few degrees of freedom that a levitated object has. While work in the field has strongly focused on the three translational degrees of freedom of this system, it has become increasingly important to understand the induced rotational motion of levitated objects, particularly in optical trapping fields, but also in magnetic and electric traps. These additional three degrees of freedom, which are intrinsic to levitated systems, offer a new set of optomechanical nonlinear interactions that lead to a rich and yet largely unexplored roto-translational motion. The control and utilization of these interactions promise to extend the utility of levitated optomechanics in both fundamental studies and applications. In this review, we provide an overview of levitated optomechanics, before focusing on the roto-translational motion of optically levitated anisotropic objects. We first present a classical treatment of this induced motion, bridging the gap between classical and quantum formalisms. We describe the different types of roto-translational motion for different particle shapes via their interaction with polarized optical trapping fields. Subsequently, we provide an overview of the theoretical and experimental approaches as well as applications that have established this new field. The review concludes with an outlook of promising experiments and applications, including the creation of non-classical states of roto-translational motion, quantum-limited torque sensing and particle characterization methods.
Rademacher, M., A. Pontin, J. M. H. Gosling, P. F. Barker, and M. Toroš. “Roto-translational optomechanics.” arXiv:2507.20905 (2025).
Diamagnetic levitation offers a promising platform for high-precision sensing, tests of dark-matter theories, and macroscopic quantum superpositions. It is unique in being completely passive, capable of levitating massive objects at room temperature. A long-standing challenge, however, is motional damping caused by eddy currents — induced currents from time-varying magnetic flux in conductors.
In earlier work, we suppressed eddy-current damping in the center-of-mass motion of a millimeter-sized levitated oscillator, achieving quality factors up to 10^5 [Appl. Phys. Lett. 122, 9 (2023); Appl. Phys. Lett. 124, 12 (2024)].
In this talk, I will focus on our recent result: an ideal axially symmetric rotor exhibits zero eddy-current damping [arXiv:2505.09895]. This demonstrates a macroscopic levitated rotor with extremely low rotational loss, opening a route to fully suppress rotor damping. Such ultra-low-loss rotors could enable next-generation gyroscopes, pressure sensors, and tests of fundamental physics.
Coffee and Tea at the Quantum Cafe
Discussions
Optical levitation in ultra-high vacuum (UHV) and cryogenic environments provides a platform potentially capable of providing quantum coherences of tens to hundreds of milliseconds for objects such as silica nano-spheres. Demonstration of matter-wave interference with optically levitated nanospheres has the potential to extend the current limit on matter-wave interference by three to four orders of magnitude, pushing the experimental limits on matter-wave duality. This would provide pathways towards the realization of gravity-induced entanglement experiments and tests of decoherence and wave function collapse models. To preserve a coherence time of approximately 200ms, experimental challenges such as near ground state cooling of the particle’s center of mass motion, pressures below 10-13mbar, internal temperatures below 100K, and relative position stability on the order of tens of nanometers must be overcome. This apparatus additionally allows for ultra-sensitive measurements of short-range forces enabling tests of the Casimir-Polder force and possible corrections to Newtonian gravity in the sub-micron regime. In this talk, I will present the progress being made towards performing short range force measurements on the path towards a macroscopic matterwave interferometer.
In the Oosterkamp group at Leiden University we work on both magnetic levitation experiments and on cantilever experiments. Both types of experiments benefit from a cold environment and low vibration levels, which we achieve inside our dilution refrigerators. The magnetic levitation is a promising platform for a combination between quantum and gravitational effects.
We have performed a measurement of gravity of 30 aN between a levitating magnet of 0.5 mg and blocks of 2.5 kg and we would like to decrease the source mass down to milligram scales. In the meantime we are working on optimizing the detection mass, which is a levitating permanent magnet in a superconducting trap. We have performed linear feedback cooling and preliminary results show mode temperatures below 20 mK. Expanding the mode cooling could open up the quantum regime for particles with these large masses and low resonance frequencies.
Coffee and Tea at the Quantum Cafe
Optomechanics with levitated particles offers a powerful platform to
explore quantum physics at macroscopic scales, including ground-state
cooling. A major outstanding goal is to entangle the motion of two
levitated nanoparticles, creating a genuine quantum state to study
decoherence mechanisms. However, weak interactions between particles
have so far prevented this.
We address this challenge by employing electrostatic (Coulomb)
interactions between two optically trapped silica nanoparticles. We
systematically study active and passive charging methods and demonstrate
strong coupling with an interaction strength reaching 12% of the
mechanical frequency (g = 0.12\omega). We also achieve ground-state
cooling and readout of the coupled normal modes.
Since steady-state entanglement still requires significantly stronger
coupling, we propose a protocol based on optimal quantum control of
continuously measured systems with time-dependent interactions. This
approach relaxes the coupling requirements and enables unconditional
entanglement under current experimental conditions. I will talk about
the stabilisation of the strongly coupled system, feedback control of
the normal modes, and the impact of non-markovian noise near the ground
state.
I will describe the proposed Quantum Invisible Particle Sensor (QuIPS) experiment, an optomechanical laser trap surrounded by active pixel detectors, that would allow for searching for sterile neutrinos and BSM physics via weak nuclear decays. The experimental setup uses CMOS sensors to measure the direction of a beta particle emitted from a trapped nanosphere, and a scintillator detector to reconstruct its energy. When combined with the momentum impulse imparted to the trapped nanosphere, the full momenta of the weak nuclear decay products may be reconstructed allowing for probing heavy sterile neutrinos and BSM physics.
Lunch at the Frontier Food Court (vegetarian options available)
Magnetic levitation techniques promise a degree of isolation of massive particles in dynamic confinement, making it an ideal candidate for the realization of large-mass superpositions and a gravity-induced entanglement experiment. The experimental status is, however, far from ground state cooling, and the current research is mainly involved with developing trap geometries and miniaturization, and studying dissipation mechanisms. I will talk about a selection of our levitation projects.
Levitated nanorods can be useful for both classical and quantum applications. However, such systems tend to become unstable in low-pressure, resulting in particle loss. Here I will present our group’s work at KCL on levitating nanorods with varying aspect ratios, and our investigation into the instability mechanisms responsible for the particle loss.
Coffee and Tea at the Quantum Cafe
Abstract to come
Discussions
We will explore a portion of the 24-km long Rail Corridor, a recreational trail that follows the route of a fomer railway line. https://railcorridor.nparks.gov.sg/visit-rail-corridor/
Dinner
- 9:00 – 12:00 Discussions
- 12:00 – 14:00 Lunch
Mechanical resonators are highly versatile tools for hybrid quantum technologies due to their many available bosonic modes with long coherence times. In order to unlock applications such as quantum simulation and sensing, however, it is necessary to develop tools for the preparation and detection of mechanical quantum states. In this talk, I will report our results on realising scalable and programmable approaches to prepare and characterize a variety of non-classical states of motion in the resonator. These techniques will find applications in the simulation of many-body Hamiltonians and in quantum metrology. Moreover, due to its microgram-scale mass, our systems have the potential to explore the interplay between quantum mechanics and gravity.
Macroscopic spatial quantum superpositions could be used to increase the sensitivity of quantum sensors, explore the boundary between quantum and classical physics and test fundamental physics. In the quest to increase the size of spatially superposed masses, there are several avenues to pursue. We will set out a new protocol for creating superpositions in a dual-frequency linear Paul trap. In this setup an ion that is co-trapped with a nanoparticle is used to manipulate the nanoparticle motional state, resulting in an entangled state of the ion spin/motion with the nanoparticle.
Quantum field theories and classical general relativity accurately model all observations to date. Although theoretically, quantum gravity is much studied, it has no empirical evidence yet. This makes “is spacetime/gravity quantum?” one of our most important open questions. I have pioneered an ambitious idea with my collaborators “spin entanglement witness for quantum gravity,” to test the quantum nature of gravity in a lab. It exploits quantum information ideas and combines a quantum spin with cooling/trapping quantum technologies. It is based on entangling two neutral quantum masses solely by their gravitational interaction while all other interactions are mitigated, e.g. electromagnetic (EM) interactions between the masses. It proves the quantum nature of gravity, as classical gravity cannot mediate quantum correlations (entanglement). The potentially realisable protocol requires meeting a rich set of challenges: mitigating the EM interactions and background, creating spatial quantum superpositions for massive objects, and measuring spin correlations to witness the entanglement. We must also protect the quantum superpositions from heating, recoil, blackbody radiation, acceleration, seismic and gravity gradient noises.
Levitated spinning ferromagnets have been proposed as a platform to surpass the standard quantum limit in magnetometry [Phys. Rev. Lett. 116, 190801 (2016)]. In this talk, I will present a microscopic Hamiltonian framework that captures their intrinsic spin–lattice dynamics. Numerical simulations [arXiv:2503.00728] reveal the origin of the characteristic t-3/2 magnetic field sensitivity scaling and quantify noise from internal spin-lattice interactions. We further show that classical dynamics of a levitated ferromagnet can reproduce the Berry phase in adiabatically rotating fields. Finally, I will discuss how spin–lattice coupling enables the generation of macroscopic spin superposition states, characterized by Wigner negativity and macroscopicity measures, and assess their robustness against decoherence. These results establish levitated ferromagnets as a versatile platform for exploring macroscopic quantum phenomena and advancing quantum sensing technologies.
- 9:00 – 12:00 Discussions
- 12:00 – 13:30 Lunch
- 13:30 – 16:00 Discussions
- 9:00 – 12:00 Discussions
- 12:00 – 13:30 Lunch
- 13:30 – 16:00 Discussions
Contact
This workshop is organised by Valerio Scarani and Martine Schut at the Centre for Quantum Technologies (CQT) at the National University of Singapore. The talks will be held at CQT. If you have any questions, please contact Martine at m.schut@nus.edu.sg.
